Hissing sound under dash?

[zeuss000]

Hi Folks, I have a strange problem with my AU2 Fairmont Ghia, as the title suggests there is a faint hissing sound under the dash somewhere. It starts as soon as i start the car, sounds like a leak which i'm sure it must be, it doesn't vary when i turn the fan or air cond on, just stays the same volume and pitch. When i turn the car off it keeps hissing for about 20 secs then fades away. I can't see anything under there that it might be, i have no idea what it is coming from. Any suggestions?
Thankyou and MERRY CHRISTMAS everybody.
Ed

[UU TS50]

Hi there im not sure exactly what it was but we had simlar problem in AU2 Futura and it was a vaccum leak under the dash .I think from the aircon controls???

[Dave_Obsession]

Sounds like there is a pressure leak somewhere......it takes a few seconds to go away once you've turned the car off because the engine & cooling system is still pressurised....

I would say its probably not related to the aircon system, as you have said it makes no difference whether the fan or aircon is on or off....

Get all your hoses pressure tested ASAP, your mechanic should be able to find the problem fairly quickly!!! With any luck, its hopefully a loose clamp or something - or maybe you may even have to replace a hose, which isn't so bad.....

Best of luck with it!! Merry Xmas!!!

[tufLTD]

Probably your brake booster.

[mik]

try adjusting the heater/aircon tempreture control in a few different positions, i have a dodgey tempreture control in mine thats hisses in the full cold half cold position, mine is a vacumm leak, i switch the engine off it takes some seconds before all the vacumm is gone and hissing stops.

[fourl6]

an AU falcon (2or3) will do this if you leave air direction controls out of place (like between feet and windscreen) but being a fairmont (climate control) im not sure if it uses the same system... try changing between face and feet etc...

[zeuss000]

Hi Folks, Thankyou for all your suggestions, i have been poking around behind the dash where i can reach, very tight in there. I found where the hissing noise is coming from, it is the "Air Temperature Sensor Duct" This is a pipe like a small ( about 3/4 inch diameter) vacuum cleaner hose and connected to a small vent just to the left of the clock on the dash, weather this is a thing peculiar to an AU2 Ghia, i'm not sure if a standard fairmont has the digital control? When i removed the heater control panel and disconnected the hose there is quite a powerfull vacuum in the pipe, when i block it with my finger ( engine running ) it sucks to my finger pretty hard, the hose compresses and noise stops but it is obviously nor meant to be blocked off. Wheather there is too much suction there for some reason or what is going on i have no idea. Any idea where to go from here? I can't figure out where the other end of the pipe connects to?
Thankyou again for all your help and have a great New Years Eve!!
Ed

[deanoseb]

Hi Ed

Same issue in au Fairmont 1 right now. Found the vacuum next to the clock before I got here but haven't got any solutions yet. Have you been able to fix it?

Cheers
Deano

[Bushbasher]

Nice bit of thread mining there Deano, The chances of getting a reply from the OP after 3 1/2 years is pretty remote. If you have found the vacuum leak then it should be pretty straight forward to fix it. If it's a damaged line then usually a small piece of rubber will fix it. Cut the line where it's damaged and join it back together with the rubber hose.

[tichman]

Just wondering if there is supposed to be a piece of foam or similar in that pipe that stops the hissing noise, think from memory its supposed to have some sort of filter in it from doing dash swap on a Ea I had. I think I used foam in it which allowed air to flow through it without blocking it and causing the pipe to compress on itself whilst shutting the noise down.